PH 7.8 because I have to add water every other day

[lagatella]

It is a vinyl pool.

PH 7.8
TA 160
CYA 45

I've put the bleach in.

Your explanation of the vapor of Muriatic acid is exactly what I am seeing. I am very careful and do hold my breath like you said.

Thank you everyone for your help. Knowing I can keep the pool at 7.8 makes me worry much less.

[chem geek]

Your TA of 160 is the primary reason that your pH is high (and why, after you add acid to lower it, it rises again) and why you are frequently having to add a lot of acid. Getting your TA lower to 100 (or even 80) will help a lot in reducing the upward pH drift and acid demand. Technically what is going on is that you are outgassing carbon dioxide from your pool because it is so far out of equilibrium with air (i.e. the carbonate alkalinity is too high).

Follow the procedure at this thread to lower your alkalinity and you will be much happier as a result.

Richard